This invention relates to devices for cutting cloth and other similar sheet material spread on a supporting surface, and deals more particularly with improvements in a cutter head of the type employing as the cutting element an elongated knife reciprocated along an axis generally normal to the sheet material being cut and with improvements in the knife itself.
The general object of the invention is to provide a cutter head for cutting sheet material which is relatively inexpensive to manufacture and to maintain and which can operate reliably over long periods of service.
A further object of the invention is to provide a cutter head of the foregoing character which is particularly well adapted for use in cutting single plies of fabric or low layups of fabric at relatively high cutting speeds, but which may also be designed for cutting higher layups of fabric, the head being capable of being constructed so as to have a relatively low mass enabling it to be rapidly accelerated and decelerated with minimum power, and the head also being capable of driving the knife at a continuous high stroking speed on the order of 10,000 strokes per minute or more.
A more particular object of the invention is to provide a cutter head wherein the knife is rotatable about a theta axis to maintain it tangent to the line of cut yet wherein the motor used for driving or reciprocating the knife does not rotate about the theta axis and is drivingly connected with the knife through a differential drive eliminating the need for the conventional swivel link which is relatively massive and of complicated construction presenting maintenance problems, the elimination of the swivel mass reducing the mass driven by the knife drive motor and therefore permitting the use of a lower horsepower, less massive motor than used in previous cutter heads.
A further object of the invention is to provide a cutter head of the foregoing character using an eccentric mechanism for reciprocating the knife, the knife having a leaf spring portion which is directly connected to the eccentric member eliminating the conventional massive and failure prone connecting link and bearings joining the eccentric member to the knife.
In keeping with the foregoing object a further object of the invention is to provide such a cutter head including simple means for inhibiting fatigue failure of the leaf spring portion of the knife, such means including design of the leaf spring portion so to eliminate an area of stress concentration and parts for reducing the amplitude of vibration of the leaf spring portion.
Another object of the invention is to provide a cutter of the foregoing character wherein the knife along its lower end portion has a sharpened forward edge and the cutter head includes a simple sharpening mechanism capable, without change, of sharpening the knife by grinding the knife on the same side face during every sharpening cycle or to sharpen the knife on opposite side faces by grinding it on one side face during some sharpening cycles and on the other face during other sharpening cycles, and which sharpening mechanism also allows the angle of the ground surface or surfaces relative to the side faces of the knife to be varied, if desired.
Another object is to provide a cutter head having a guide engageable with the knife to restrain it, with minimal frictional loss, to reciprocation along a given axis.
Other objects and advantages of the invention will be apparent from the following detailed description of a preferred embodiment and from the accompanying drawings and claims.
A cutter head incorporating most or all of the features of the invention is particularly well adapted for use in an automatic cutting machine wherein the cutter head is carried by a tool carriage movable in two coordinate directions over the surface of the material being cut, and the invention is therefore hereinafter described in association with such a cutting machine. However, most of the features of the invention may be used to advantage in other cutter heads, such as the heads of hand-guided cutters, and there is accordingly no intention to limit the scope of the invention cutter heads for automatic cutting machines.